Electronic switches, typically IGBT or other similar electronic components, are sized for a given maximum current load or current rating. When it is required to provide a device capable of delivering a power such that the current exceeds the current rating on a single switch, there are provided arrangements of electronic switches in parallel, so as to split the current delivered between two or more switches rather than only one. The switches in parallel are driven by the same drive signal, for example a PWM signal. Therefore, half-bridge or full-bridge configurations are, for example, possible, where in each branch of the bridge there are provided two or more electronic switches, controlled by the same drive signal. Each electronic switch is associated with a respective driver circuit or board.
The drive signal of the electronic switches is generated by a drive signal processing circuit or processing board, typically a DSP (Digital Signal Processor). The drive signal processing circuit is connected to each drive circuit of the various electronic switches via a drive line, through which the drive signal is transmitted. Moreover, each driver circuit is connected to the drive signal processing circuit with a fault line. If a fault occurs in the electronic switch associated with a given driver circuit, the driver circuit sends a fault signal via the fault line to the drive signal processing circuit, so that, for example, the device is switched off and/or an alarm signal is emitted. The fault in the electronic switch can result from various causes. In general, the fault causes an increased voltage drop across the electronic switch. When said voltage drop exceeds a threshold value, the driver circuit generates a fault signal on the fault line.
If a fault or interruption occurs on the drive line, via which the drive signal processing circuit delivers the drive signal to the driver circuit, the respective electronic switch remains open, as it no longer receives the switching signal. When this occurs, the flow of current, which in normal operating conditions is split between the N electronic switches in parallel, is split between N−1 switches, with a consequent increase in the current rate through each remaining switch. For example, in the case of a configuration with two switches in parallel, if a fault occurs in the drive line associated with one of the electronic switches, this latter will no longer switch in closed conditions and will remain constantly open. The other switch will sustain the whole current flow in the conduction intervals. If the current exceeds the maximum allowable value on the electronic circuit, this will break. A situation of absence of drive signal is not detected by the driver circuit and therefore no alarm condition occurs. The device continues to operate until the electronic switch, which continues to receive the drive signal, is irreversibly damaged.
Therefore, there is a need to improve the reliability of devices of the type described above and in particular to verify any interruptions or malfunctioning of the drive line, to prevent irreversible damages to electronic switches. It is advisable for this function to be performed without burdening the circuits, i.e. without the need to provide additional connection lines between the drive signal processing circuit and each driver circuit of the respective electronic switch.